Hi everybody,
This is not an isolated issue: I counted 15+ threads on the Community forum with similar problems (one or more forms of notification suddenly stopped). Many date back months and even years ago, most were not (reported to be) solved. It is a systemic issue at AirBnB's side.
On 17 August 2019 I reported that suddenly I no longer got an audible alert when a push notification or SMS from AirBnB arrived. On request I sent screenshots of my AirBnB app settings and Android notification settings. AirBnB support told me 2 days later that "this is a known issue and I have forwarded your concern to our Project Engineers." To date (11 November) the problem is NOT resolved.
In fact yesterday it got worse: no notifications whatsoever from AirBnB. Like Josef47, I checked all AirBnB app and Android notifications settings - all correct. Nothing in spamfolders.